With the government shutdown, there's been concern about the availability of PubMed and other information resources.
The statement on PubMed sums up the general status: the databases are operational but are not being updated:

PubMed is open, however it is being maintained with minimal staffing due to the lapse in government funding. Information will be updated to the extent possible, and the agency will attempt to respond to urgent operational inquiries.

What's down:
Librarian Alisha Miles has put together a status update on sites of interest to the biomedical community:
http://wp.me/puPL6-kn

Among the few resources that are not available is the free government version of ERIC, the education database. Penn provides access to two other versions:http://franklin.library.upenn.edu/record.html?id=FRANKLIN_2199987
Also unavailable are the Library of Congress and the Census Bureau websites and National Library of Medicine document delivery services.

Alternatives for current citations:
Although many databases useful for biomedical research obtain citations from PubMed, they also do indexing of their own.
Consider these resources, all linked on the health sciences library homepages: